This invention relates to a method for the preparation of polycarbonate. More particularly the method relates to a method of preparing polycarbonate by the melt reaction of at least one dihydroxy aromatic compound with at least one diaryl carbonate, said melt reaction being mediated by a transesterification catalyst, said transesterification catalyst comprising at least one mixed alkali metal salt of phosphoric acid and a co-catalyst.
Conventionally, polycarbonate is prepared by the reaction of a dihydroxy aromatic compound such as bisphenol A with phosgene in the presence of an aqueous phase comprising an acid acceptor such as sodium hydroxide and an organic solvent such as dichloromethane. Typically, a phase transfer catalyst, such as a quaternary ammonium compound or a low molecular weight tertiary amine, such as triethylamine is added to the aqueous phase to enhance the polymerization rate. This synthetic method is commonly known as the xe2x80x9cinterfacialxe2x80x9d method for preparing polycarbonate.
The interfacial method for making polycarbonate has several inherent disadvantages. First it is a disadvantage to operate a process which requires phosgene as a reactant due to obvious safety concerns. Second it is a disadvantage to operate a process which requires using large amounts of an organic solvent because elaborate precautions must be taken to prevent adventitious release of the volatile solvent into the environment. Third, the interfacial method requires a relatively large amount of equipment and capital investment. Fourth, the polycarbonate produced by the interfacial process is prone to having inconsistent color, higher levels of particulates, and higher chlorine content, which can cause corrosion.
More recently polycarbonate has been prepared on a commercial scale in a solventless process involving the transesterification reaction between a dihydroxy aromatic compound (e.g. bisphenol A) and a diaryl carbonate (e.g., diphenyl carbonate) in the presence of a transesterification catalyst. This reaction is performed in a molten state in the absence of solvent, and is driven to completion by mixing the reactants under reduced pressure and high temperature with simultaneous distillation of the phenol by-product produced by the reaction. This method of preparing polycarbonate is referred to as the xe2x80x9cmeltxe2x80x9d process. In some respects the melt process is superior to the interfacial method because it does not employ phosgene, it does not require a solvent, and it uses less equipment. Moreover, the polycarbonate produced by the melt process does not contain chlorine contamination from the reactants, has lower particulate levels, and has a more consistent color. Therefore it is highly desirable to use the melt process when making polycarbonate in commercial manufacturing processes.
A wide variety of transesterification catalysts have been evaluated for use in the preparation of polycarbonate using the melt process. Alkali metal hydroxides, in particular sodium hydroxide, have proven to be particularly effective as transesterification catalysts. However, while alkali metal hydroxides are useful polymerization catalysts, they are also known to promote Fries reaction along the growing polycarbonate chains which results in the production of branched polycarbonate products. The presence of branching sites within a polycarbonate chain can causes changes in the melt flow behavior of the polycarbonate, which can lead to difficulties in processing.
It would be desirable, therefore, to develop a catalyst system which effects melt polymerization while minimizing undesirable reaction products, such as branched side reaction products.
In one aspect, the present invention provides a method of preparing polycarbonate, said method comprising reacting under melt polymerization conditions in the presence of a transesterification catalyst at least one dihydroxy aromatic compound and at least one diaryl carbonate, said transesterification catalyst comprising at least one mixed alkali metal salt of phosphoric acid and at least one co-catalyst, said co-catalyst comprising a quaternary ammonium salt, a quaternary phosphonium salt or a mixture thereof.
In another aspect, the present invention relates to polycarbonates prepared by the method of the present invention, said polycarbonates having lower levels of Fries product than polycarbonates prepared by conventional melt polymerization methods.
The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included herein. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.
The singular forms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise.
xe2x80x9cOptionalxe2x80x9d or xe2x80x9coptionallyxe2x80x9d means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not.
As used herein the term xe2x80x9cpolycarbonatexe2x80x9d refers to polycarbonates incorporating structural units derived from one or more dihydroxy aromatic compounds and includes copolycarbonates and polyester carbonates.
As used herein, the term xe2x80x9cmelt polycarbonatexe2x80x9d refers to a polycarbonate made by the transesterification of at least one diaryl carbonate with at least one dihydroxy aromatic compound.
xe2x80x9cBPAxe2x80x9d is herein defined as bisphenol A and is also known as 2,2-bis(4-hydroxyphenyl)propane, 4,4xe2x80x2-isopropylidenediphenol and p,p-BPA.
As used herein, the term xe2x80x9cbisphenol A polycarbonatexe2x80x9d refers to a polycarbonate in which essentially all of the repeat units comprise a bisphenol A residue.
As used herein, the term xe2x80x9cpolycarbonatexe2x80x9d includes both high molecular weight polycarbonate and oligomeric polycarbonate. High molecular weight polycarbonate is defined herein as having number average molecular weight, Mn, greater than 8000 daltons, and an oligomeric polycarbonate are defined as having number average molecular weight, Mn, less than 8000 daltons.
As used herein the term xe2x80x9cpercent endcapxe2x80x9d refers to the percentage of polycarbonate chain ends which are not hydroxyl groups. In the case of bisphenol A polycarbonate prepared from diphenyl carbonate and bisphenol A, a xe2x80x9cpercent endcapxe2x80x9d value of about 75% means that about seventy-five percent of all of the polycarbonate chain ends comprise phenoxy groups while about 25% of said chain ends comprise hydroxyl groups. The terms xe2x80x9cpercent endcapxe2x80x9d and xe2x80x9cpercent endcappingxe2x80x9d are used interchangeably.
As used herein the term xe2x80x9caromatic radicalxe2x80x9d refers to a radical having a valence of at least one and comprising at least one aromatic ring. Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, and biphenyl. The term includes groups containing both aromatic and aliphatic components, for example a benzyl group, a phenethyl group or a naphthylmethyl group. The term also includes groups comprising both aromatic and cycloaliphatic groups for example 4-cyclopropylphenyl and 1,2,3,4-tetrahydronaphthalen-1-yl.
As used herein the term xe2x80x9caliphatic radicalxe2x80x9d refers to a radical having a valence of at least one and consisting of a linear or branched array of atoms which is not cyclic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of aliphatic radicals include methyl, methylene, ethyl, ethylene, hexyl, hexamethylene and the like.
As used herein the term xe2x80x9ccycloaliphatic radicalxe2x80x9d refers to a radical having a valance of at least one and comprising an array of atoms which is cyclic but which is not aromatic, and which does not further comprise an aromatic ring. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of cycloaliphatic radicals include cyclopropyl, cyclopentyl cyclohexyl, 2-cyclohexylethy-1-yl, tetrahydrofuranyl and the like.
As used herein the term xe2x80x9cFries productxe2x80x9d is defined as a structural unit of the product polycarbonate which upon hydrolysis of the product polycarbonate affords a carboxy-substituted dihydroxy aromatic compound bearing a carboxy group adjacent to one or both of the hydroxy groups of said carboxy-substituted dihydroxy aromatic compound. For example, in bisphenol A polycarbonate prepared by a melt reaction method in which Fries reaction occurs, the Fries product includes those structural features of the polycarbonate which afford 2-carboxy bisphenol A upon complete hydrolysis of the product polycarbonate.
The terms xe2x80x9cFries productxe2x80x9d and xe2x80x9cFries groupxe2x80x9d are used interchangeably herein.
The terms xe2x80x9cFries reactionxe2x80x9d and xe2x80x9cFries rearrangementxe2x80x9d are used interchangeably herein.
As used herein the term xe2x80x9cFries levelxe2x80x9d refers to the amount of Fries product present in a product polycarbonate.
As mentioned, the present invention relates to a method of preparing polycarbonate, said method comprising reacting under melt polymerization conditions in the presence of a transesterification catalyst at least one dihydroxy aromatic compound and at least one diaryl carbonate, said transesterification catalyst comprising at least one mixed alkali metal salt of phosphoric acid and at least one co-catalyst, said co-catalyst comprising a quaternary ammonium salt, a quaternary phosphonium salt or a mixture thereof. The mixed alkali metal salt comprises at least two different alkali metal ions selected from the group consisting of cesium ions, sodium ions, and potassium ions. Such mixed alkali metal phosphate catalysts are conveniently prepared by addition of a first alkali metal hydroxide to an aqueous solution of phosphoric acid followed by the addition of a second alkali metal hydroxide to the mixture. Such additions are conveniently carried out as titrations in which the amounts of alkali metal hydroxides added may be monitored by a change in the pH of the phosphoric acid solution. For example, an aqueous solution of phosphoric acid is first treated with about 0.95 equivalents of cesium hydroxide and subsequently with 0.6 equivalents of sodium hydroxide. The resultant aqueous solution comprises the mixed alkali metal phosphate CsNaHPO4, which has been found to possess improved catalytic properties over other alkali metal phosphates containing only a single species of alkali metal ion. Typically, the mixed alkali metal phosphate catalyst is added to the polymerization as an aqueous solution. Thus, the preparation and use of the mixed alkali metal phosphate catalysts of the present invention is especially convenient.
When the mixed alkali metal phosphate catalyst comprises cesium and sodium ions it has been found that catalytic activity is optimal when said catalyst comprises between about 0.85 and about 1.0 equivalents of cesium and about 0.1 to about 0.6 equivalents of sodium per phosphoric acid equivalent. When the mixed alkali metal phosphate catalyst comprises potassium and sodium ions it has been found that catalytic activity is optimal when said catalyst comprises between about 0.85 and about 1.0 equivalents of potassium and about 0.1 to about 1 equivalents of sodium per phosphoric acid equivalent.
In melt a polymerization reaction of one or more dihydroxy aromatic compounds and one or more diaryl carbonates, the mixed alkali metal salt of phosphoric acid is typically employed in an amount corresponding to between about 1xc3x9710xe2x88x928 and about 1xc3x9710xe2x88x923, preferably about 1xc3x9710xe2x88x926 and about 2.5xc3x9710xe2x88x924 moles of mixed alkali metal salt of phosphoric acid per mole dihydroxy aromatic compound.
The dihydroxy aromatic compounds used according to the method of the present invention may be dihydroxy benzenes, for example hydroquinone (HQ), 2-methylhydroquinone, resorcinol, 5-methylresorcinol and the like; dihydroxy naphthalenes, for example 1,4-dihydroxynathalene, 2,6-dihydroxynaphthalene, and the like; and bisphenols, for example bisphenol A and 4,4xe2x80x2-sulfonyldiphenol. Typically, the dihydroxy aromatic compound comprises at least one bisphenol having structure I 
wherein R1 is independently at each occurrence a halogen atom, nitro group, cyano group, C1-C20 alkyl group, C4-C20 cycloalkyl group, or C6-C20 aryl group; n and m are independently integers 0-4; and W is a bond, an oxygen atom, a sulfur atom, a SO2 group, a C1-C20 aliphatic radical, a C6-C20 aromatic radical, a C6-C20 cycloaliphatic radical or the group 
wherein R2 and R3 are independently a hydrogen atom, C1-C20 alkyl group, C4-C20 cycloalkyl group, or C4-C20 aryl group; or R2 and R3 together form a C4-C20 cycloaliphatic ring which is optionally substituted by one or more C1-C20 alkyl, C6-C20 aryl, C5-C21 aralkyl, C5-C20 cycloalkyl groups or a combination thereof.
Bisphenols having structure I are illustrated by bisphenol A; 2,2-bis(4-hydroxy-3-methylphenyl)propane; 2,2-bis(3-chloro-4-hydroxyphenyl)propane; 2,2-bis(3-bromo-4-hydroxyphenyl)propane; 2,2-bis(4-hydroxy-3-isopropylphenyl)propane; 1,1-bis(4-hydroxyphenyl)cyclohexane; 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane; 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and the like.
Typically, the diaryl carbonate used is at least one diaryl carbonate having structure II 
wherein R4 is independently at each occurrence a halogen atom, nitro group, cyano group, C1-C20 alkyl group, C1-C20 alkoxy carbonyl group, C4-C20 cycloalkyl group, or C6-C20 aryl group; and t and v are independently integers 0-5.
Diaryl carbonates II are illustrated by diphenyl carbonate, bis(4-methylphenyl)carbonate, bis(4-chlorophenyl) carbonate, bis(4-fluorophenyl) carbonate, bis(2-chlorophenyl) carbonate, bis(2,4-difluorophenyl) carbonate, bis(4-nitrophenyl)carbonate, bis(2-nitrophenyl) carbonate, bis(methyl salicyl) carbonate, and the like.
The transesterification catalyst used according to method of the present invention comprises at least one co-catalyst, said co-catalyst being present in an amount corresponding to between about 1xc3x9710xe2x88x926 and about 1xc3x9710xe2x88x922, preferably between about 1xc3x9710xe2x88x925 and about 2.5 10xe2x88x924 moles of co-catalyst per mole of dihydroxy aromatic compound employed. Typically, the co-catalyst is at least one quaternary ammonium salt, at least one quaternary phosphonium salt, or a mixture thereof.
In one embodiment of the present invention the co-catalyst is a quaternary ammonium compound having structure III 
wherein R5-R8 are independently a C1-C20 alkyl group, C4-C20 cycloalkyl group, or a C4-C20 aryl group; and Xxe2x88x92 is an organic or inorganic anion. Typically the anion Xxe2x88x92 is selected from the group consisting of hydroxide, halide, carboxylate, phenoxide, sulfonate, sulfate, carbonate, and bicarbonate. Hydroxide is frequently preferred. Quaternary ammonium salts having structure III are illustrated by tetramethylammonium hydroxide, tetrabutylammonium hydroxide, and the like.
In an alternate embodiment of the present invention the co-catalyst is a quaternary phosphonium compound having structure IV 
wherein R9-R12 are independently a C1-C20 alkyl group, C4-C20 cycloalkyl group, or a C4-C20 aryl group; and Xxe2x88x92 is an organic or inorganic anion. Typically the anion Xxe2x88x92 is selected from the group consisting of hydroxide, halide, carboxylate, phenoxide, sulfonate, sulfate, carbonate, and bicarbonate. Hydroxide is frequently preferred. Quaternary phosphonium salts having structure IV are illustrated by tetrabutylphosphonium hydroxide, tetraoctylphosphonium hydroxide, tetrabutylphosphonium acetate, and the like.
In structures III and IV, the anion Xxe2x88x92 is typically an anion selected from the group consisting of hydroxide, halide, carboxylate, phenoxide, sulfonate, sulfate, carbonate, and bicarbonate. With respect to transesterifcation catalysts comprising co-catalysts having structures III and IV, where Xxe2x88x92 is a polyvalent anion such as carbonate or sulfate it is understood that the positive and negative charges in structures III and IV are properly balanced. For example, in tetrabutylphosphonium carbonate where R9-R12 in structure IV are each butyl groups and Xxe2x88x92 represents a carbonate anion, it is understood that Xxe2x88x92 represents xc2xd (CO3xe2x88x922).
The term xe2x80x9cmelt polymerization conditionsxe2x80x9d is understood to mean those conditions necessary to effect reaction between a diaryl carbonate and a dihydroxy aromatic compound in the presence of a transesterification catalyst. The reaction temperature is typically in the range of about 100xc2x0 C. to about 350xc2x0 C., more preferably about 180xc2x0 C. to about 310xc2x0 C. The pressure may be at atmospheric pressure, supra-atmospheric pressure, or a range of pressures from atmospheric pressure to about 15 torr in the initial stages of the reaction, and at a reduced pressure at later stages, for example in the range of about 0.2 to about 15 torr. The reaction time is generally about 0.1 hours to about 10 hours.
The method of the present invention may be conducted as a batch process or as a continuous process. In either case, the melt polymerization conditions used may comprise two or more distinct reaction stages, for example, a first reaction stage in which the starting diaryl carbonate and dihydroxy aromatic compound are converted into an oligomeric polycarbonate and a second reaction stage wherein the oligomeric polycarbonate formed in the first reaction stage is converted to high molecular weight polycarbonate. Such xe2x80x9cstagedxe2x80x9d polymerization reaction conditions are especially suitable for use in continuous polymerization systems wherein the starting monomers are oligomerized in a first reaction vessel and the oligomeric polycarbonate formed therein is continuously transferred to one or more downstream reactors in which the oligomeric polycarbonate is converted to high molecular weight polycarbonate. Typically, in the oligomerization stage the oligomeric polycarbonate produced has a number average molecular weight of from about 1000 to about 7500 daltons. In one or more subsequent polymerization stages the number average molecular weight of the polycarbonate is increased to between about 8000 and about 25000 daltons.
In one embodiment, the process is conducted as a two stage process. In the first stage of this embodiment, the co-catalyst, for example tetramethylammonium hydroxide is introduced into the reaction system comprising the dihydroxy aromatic compound and the diaryl carbonate. The first stage is conducted at a temperature of 270xc2x0 C. or lower, preferably between about 150xc2x0 C. and about 250xc2x0 C., more preferably between about 150xc2x0 C. and about 230xc2x0 C. The duration of the first stage is preferably from about 2 minutes to about 5 hours, even more preferably about 2 minutes to about 3 hours at a pressure form atmospheric pressure to 100 torr. It is generally preferable that oxygen be excluded from the reaction mixture during the oligomerization and subsequent polymerization stages. Oxygen exclusion is conveniently achieved using known techniques, for example, maintaining a positive pressure of nitrogen in the system before and after evacuation.
The mixed alkali metal salt of phosphoric acid may be added in the first stage along with the co-catalyst. Alternatively the mixed alkali metal salt of phosphoric acid is introduced into the product from the first stage and further polycondensation is conducted. The salt of the mixed alkali metal salt of phosphoric acid may be added in its entire amount in the second stage, or it may be added in batches in the second and subsequent stages so that the total amount is within the aforementioned ranges.
It is preferable in the second and any subsequent stages of the polycondensation step for the reaction temperature to be raised while the reaction system is reduced in pressure compared to the first stage. Typically, in the late stages of the polymerization reaction the reaction mixture is heated at temperatures in a range between about 240xc2x0 C. and 320xc2x0 C. under reduced pressure of about 5 mm Hg or less, and preferably 1 mm Hg or less.
In one embodiment of the present invention at least one dihydroxy aromatic compound and at least one diaryl carbonate are reacted in the presence of a transesterification catalyst under melt polymerization conditions in the presence of a branching agent to produce a product polycarbonate which is branched. Typically, the branching agent may be a trisphenol such as 1,1,1-tris(4-hydroxyphenyl)ethane, THPE. Other branching agents suitable for use according to the method of the present invention include triacids such as trimellitic acid, 9-carboxyoctadecandioic acid, and the corresponding phenyl esters thereof. Typically, the branching agent is used in an amount corresponding to about 0.001 to about 0.03 moles of branching agent per mole of dihydroxy aromatic compound.
Additionally, the method of the present invention may carried out in the presence of an endcapping agent. Thus, at least one endcapping agent, at least one dihydroxy aromatic compound, at least one diaryl carbonate, and at least one transesterification catalyst, said transesterification catalyst comprising at least one mixed alkali metal salt of phosphoric acid and at least one co-catalyst, are reacted under melt polymerization conditions to provide a product polycarbonate comprising terminal groups derived from the endcapping agent. Typically, the endcapping agent is a monofunctional phenol such as cardanol, p-cresol, p-tert-butylphenol, and p-cumylphenol. For example when p-tert-butylphenol is used as the endcapping agent the product polycarbonate prepared according to the method of the present invention comprises terminal p-tert-butylphenoxy groups.
In some aspects the method of the present invention is superior to earlier melt polymerization methods based upon the speed at which the polymerization reaction occurs under the influence of the mixed alkali metal phosphate catalyst co-catalyst combination employed. Thus, higher molecular weight product polycarbonates are obtained in a shorter period of time. Additionally, the product polycarbonates prepared according to the method of the present invention typically possess lower levels of Fries product than product polycarbonates prepared under comparable conditions of reaction time, reaction temperature, catalyst loading and the like, using conventional catalyst systems. In general, it is desirable to limit the amount of Fries product present in the product polycarbonate to the greatest extent possible since high Fries levels can produce discoloration and serve as sites for uncontrolled polymer branching which can affect the melt flow properties of the product polycarbonate. Generally, the level of Fries rearrangement product present in high molecular weight polycarbonate prepared according to the method of the present invention is less than about 1000 parts per million, preferably less than 500 parts per million.
It is understood, especially for melt reactions of the type presented in the instant invention, that the purity of the monomers employed may strongly affect the properties of the product polycarbonate. Thus, it is frequently desirable that the monomers employed be free of, or contain only very limited amounts of, contaminants such as metal ions, halide ions, acidic contaminants and other organic species. This may be especially true in applications such as optical disks, (e.g. compact disks) where contaminants present in the polycarbonate can affect disk performance. Typically the concentration of metal ions, for example iron, nickel, cobalt, sodium, and postassium, present in the monomer should be less than about 10 ppm, preferably less than about 1 ppm and still more preferably less than about 100 parts per billion (ppb). The amount of halide ion present in the polycarbonate, for example fluoride, chloride and bromide ions, should be minimized in order to inhibit the absorption of water by the product polycarbonate as well as to avoid the corrosive effects of halide ion on equipment used in the preparation of the polycarbonate. Certain applications, for example optical disks, may require very low levels of halide ion contaminants. Preferably, the level of halide ion present in each monomer employed should be less than about 1 ppm. The presence of acidic impurities, for example organic sulfonic acids which may be present in bisphenols such as BPA, should be minimized since only minute amounts of basic catalysts are employed in the oligomerization and subsequent polymerization steps. Even a small amount of an acidic impurity may have a large effect on the rates of oligomerization and polymerization since it may neutralize a substantial portion of the basic co-catalyst employed. Lastly, the tendency of polycarbonates to degrade at high temperature, for example during molding, with concomitant loss of molecular weight and discoloration correlates strongly with the presence of contaminating species within the polycarbonate. In general, the level of purity of a product polycarbonate prepared using a melt reaction method such as the instant invention will closely mirror the level of purity of the starting monomers.
The polycarbonate made by the method of the present invention may optionally be blended with any conventional additives, including but not limited to dyestuffs, UV stabilizers, antioxidants, heat stabilizers, and mold release agents, in order to facilitate the formation and use of a molded article. In particular, it is preferable to form a blend of the polycarbonate made by the method of the present invention and additives which serve as process aids during the molding process and which confer additional stability upon the molded article. The blend may optionally comprise from about 0.0001 to about 10% by weight of the desired additives, more preferably from about 0.0001 to about 1.0% by weight of the desired additives.
Substances or additives which may be added to the polycarbonate of this invention, include, but are not limited to, heat-resistant stabilizers, UV absorbers, mold-release agents, antistatic agents, slip agents, antiblocking agents, lubricants, anticlouding agents, coloring agents, natural oils, synthetic oils, waxes, organic fillers, inorganic fillers, and mixtures thereof.
Examples of the aforementioned heat-resistant stabilizers, include, but are not limited to, phenol stabilizers, organic thioether stabilizers, organic phosphite stabilizers, hindered amine stabilizers, epoxy stabilizers and mixtures thereof. The heat-resistant stabilizer may be added in the form of a solid or liquid.
Examples of UV absorbers include, but are not limited to, salicylic acid UV absorbers, benzophenone UV absorbers, benzotriazole UV absorbers, cyanoacrylate UV absorbers, and mixtures thereof.
Examples of the mold-release agents include, but are not limited to natural and synthetic paraffins, polyethylene waxes, fluorocarbons, and other hydrocarbon mold-release agents; stearic acid, hydroxystearic acid, and other higher fatty acids, hydroxyfatty acids, and other fatty acid mold-release agents; stearic acid amide, ethylenebisstearamide, and other fatty acid amides, alkylenebisfatty acid amides, and other fatty acid amide mold-release agents; stearyl alcohol, cetyl alcohol, and other aliphatic alcohols, polyhydric alcohols, polyglycols, polyglycerols and other alcoholic mold release agents; butyl stearate, pentaerythritol tetrastearate, and other lower alcohol esters of fatty acid, polyhydric alcohol esters of fatty acid, polyglycol esters of fatty acid, and other fatty acid ester mold release agents; silicone oil and other silicone mold release agents, and mixtures of any of the aforementioned.
The coloring agent may be either pigments or dyes. Inorganic coloring agents and organic coloring agents may be used separately or in combination in the invention.